[MPEG-OTSPEC] Shared GSUB/GPOS notes, was Re: dmap proposal

[John Hudson]

On 2023-12-27 3:19 am, Skef Iterum wrote:
>
> Some preliminary notes on an idea I'm looking info, starting from this 
> line of reasoning:
>
>  1. My worry about using dmap for multi-language/region support is
>     that the solution is separate from the script/language GSUB/GPOS
>     mechanism. *Ideally we want fonts that support different scripts
>     and languages via the latter*, and doing so while starting with
>     different initial cmaps is a lot of work and QA.
>
Do we? The langsys mechanism in OTL has proven to be unreliable for 
coming up on thirty years, such that we now recommend to clients having 
separate fonts for individual languages if differences in glyph shape or 
behaviour are considered critical. The chain of things that document 
creators and software need to get right to ensure correct display of 
langsys-specific GSUB or GPOS is too fragile to be reliable, while 
selecting a clearly labeled font targeting a specific language is much 
more robust. Hence, e.g. Tiro Devanagari Hindi, Tiro Devanagari Marathi, 
and Tiro Devanagari Sanskrit.

We already make some TTCs with distinct cmap tables, and some with 
distinct GSUB tables, so if I understand your proposal correctly it is, 
like Peter’s DMAP proposal, a data and processing efficiency measure, 
correct? A mechanism that does this at the initial character-to-glyph 
mapping would seem to provide more robust language-specific support.

JH


-- 

John Hudson
Tiro Typeworks Ltdwww.tiro.com

Tiro Typeworks is physically located on islands
in the Salish Sea, on the traditional territory
of the Snuneymuxw and Penelakut First Nations.

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